The Perspective of Evolution

It is a general feature of evolution that later developments have to build on previous stages. In terms of anatomy the recurrent laryngeal nerve is the classic example of a limitation imposed by a previous stage of evolution. In fish this nerve supplied the gills. It passed to the gills behind their supply of blood vessels. As animals developed higher up the evolutionary tree the recurrent laryngeal nerve still supplied the throat area despite the fact that this region had moved forward to the head in most animals. Today, even in the giraffe, this nerve passes down the neck and under blood vessels near to the heart, and then all the way back up the neck of the giraffe to the larynx. Nature has never enabled this nerve to take a shorter route to the larynx and is limited by the animal’s past history.

This aspect of evolution, that future developments must use past structures and functions, is true at all levels. When we come to the evolutionary development of monkeys and apes we will find this in action. Very often we find that a structure which existed for one function becomes adapted for another use when the environment demands it. The emphasis here is on structure rather than on the conscious aspect because the conscious dimension and structure are closely intertwined and therefore changes in structure are a good guide to the mental capacities of the animal.

We see clearly how structure changed when the tree shrew took to the trees and formed the earliest ancestor of the monkeys and lemurs. The new environment in the trees put demands on these animals and the ones with more favoured adaptions survived and were successful in breeding. Over time a number of important adaptations occurred. The new environment made greater demands on the sense of balance as these animals began to climb among the trees. The development of the opposable thumb enabled them to grasp better. The development of binocular vision, enabling three dimensional sight, improved their ability to move through the trees. Binocular vision was accompanied by the ability to see colour which enabled them to distinguish suitable foods and avoid poisonous things. Curiosity was also important at this stage. All these developments were a consequence of living in a more demanding environment.

We must not pass on from the development of colour vision without discussing the fact that monkeys get very agitated when placed in red rooms. It has been suggested that the origin of this dates back to their experiences in the jungle where the first light of the morning had a red hue and it was at this time that they were most vulnerable to attack. The argument is that somehow the colour red has acquired a warning quality. It is debatable whether the above theory is correct, but it is true that red catches human attention and is often used in warning signs. In nature red snakes and insects are treated as poisonous, as are red toadstools. However, red berries are a popular food for birds as are red fruit for human consumption. The situation is therefore not simple. It may be that there is something basic about the conscious perception of red that does not reduce to easy explanations: red is just red, blue is just blue, green is just green and yellow is just yellow.

As early man developed from the monkeys and apes, the climate changed and so changes took place in their habits making it necessary for them to travel from one food source to another and man gradually developed the capacity to stand and walk upright. You will have noted how important the earlier developments in balance were to this new task. The development of the opposable thumb also found further use in tool manipulation, which in its simplest form can be seen in monkeys using stones to crack open nuts. This development was to prove pivotal and the basis of much human ability to mould the environment and keep records. With it the touch and motor areas of the cerebrum increased in size and complexity.